The present invention relates to the drying of particulate material, and in particular to the drying of particulate sugar beet pulp.
According to the teachings of the present invention, the efficiency of the drying of particulate material may be improved by 10-15%, and possibly even more, when comparing the operation of a steam dryer according to the present invention with the operation of a steam dryer according to the prior art, for example steam dryers disclosed in EP 0 153 704, EP 0 537 262(A1), EP 0 955 511 (A3), EP 1 044 044 (A1), EP 1 070 223 (A1), EP 1 956 326 (B1), EP 2 457 649 (A1), U.S. Pat. No. 4,813,155, U.S. Pat. No. 5,357,686 (A), U.S. Pat. No. 6,154,979(A), U.S. Pat. No. 6,266,895(B1), U.S. Pat. No. 6,438,863(B1), U.S. Pat. No. 6,966,466(B2), U.S. Pat. No. 7,578,073 (B2) and WO2010139331(A2).
Reference is made to the above patent applications and patents, and the above US patents are hereby incorporated in the present specification by reference.
It is an object of the present invention to improve the efficiency in drying particulate material. In particular, it is an object of the present invention to improve the energy efficiency of a steam dryer for drying particulate sugar beet pulp.
The above objects are according to a first aspect of the present invention achieved by a method of drying humid particulate material, the method comprising:
providing a supplier of pressurized steam, and a steam dryer for drying the humid particulate material,
the steam dryer comprising: a closed container maintaining an atmosphere comprising superheated steam at an elevated pressure, the closed container comprising a lower cylindrical part and an upper cylindrical part, a heat exchanger assembly located inside the closed container and comprising a channel for allowing the superheated steam to be transported from inside the upper cylindrical part to inside the lower cylindrical part, the heat exchanger assembly comprising a first heat exchanger and a second heat exchanger for heating the superheated steam, the first heat exchanger being positioned above the second heat exchanger and the channel going down through the first and second heat exchangers and a plurality of guide plates positioned upright and circumferentially around the heat exchanger;
the method comprising: supplying a primary flow of steam from the supplier to the second heat exchanger for heating the second heat exchanger and condensing the primary flow of steam within the second heat exchanger into a flow of condensed hot water; discharging the flow of condensed hot water from the second heat exchanger, generating a first flow of fluid exclusively from the flow of condensed hot water; leading the first flow of fluid to the first heat exchanger for heating the first heat exchanger; generating a flow of the superheated steam by means of an impeller going upwards on the outside of the heat exchanger assembly to the inside of the upper cylindrical part and downwards through the channel; feeding the humid particulate material into the lower cylindrical part of the closed container; guiding the humid particulate material by means of the plurality of guide plates positioned upright and circumferentially around the heat exchanger along a path around the heat exchanger assembly for subjecting the humid particulate material to the flow of the superheated steam for converting the humid particulate material into dry particulate material; and removing the dry particulate material from the closed container.
According to the basic teachings of the present invention, the improvement of the efficiency of the drying of particulate material by using a steam dryer is improved by more than 10%, such as 10-15%, or possibly even more by employing a heat exchanger assembly comprising at least two separate heat exchangers or heat exchanger sections positioned so that the one being the first heat exchanger or heat exchanger section is positioned above the second heat exchanger or heat exchanger section, and the heating medium, i.e., the steam introduced into the heat exchanger assembly, being input to the second or lower heat exchanger or heat exchanger section, the water discharge from which is used for generating a flow of fluid, i.e., steam or hot water input to the first heat exchanger or heat exchanger section, i.e., the upper-most located heat exchanger or heat exchanger section. The use of the heat exchanger assembly according to the present invention has surprisingly brought about substantive efficiency improvements, which improvement or use of two heat exchangers or two separate heat exchanger sections in accordance with the teachings of the present invention is not known to have been disclosed beforehand.
Examples of moist particulate material, normally non-homogenous materials suitable for being dried in accordance with the teachings of the present invention are: wood chips, wood pulp, bark chips, sugar beet pulp, sludge, wet distillers grain, bagasse, chopped or otherwise particulate material of alfalfa or other plants or vegetables, fish meal or the like, or even combinations of the above materials with other ingredients or materials. Preferably, the particulate material is sugar beet pulp.
The supplier of steam may be a boiler, or an outlet of steam in another system utilizing pressurized steam, for example, an outlet of a turbine.
The generating of the first flow of fluid may comprise forming the first flow of fluid comprising the flow of condensed hot water or at least a part of the condensed hot water. This way, the first heat exchanger will be fed by hot water having a lower temperature than the steam fed to the second heat exchanger. The flow of the superheated steam passes through the first heat exchanger before it reaches the second heat exchanger. This means that the first heat exchanger effectively has the function of a pre-heater, which improves the efficiency. Alternatively, the generating of the first flow of fluid may comprise separating the flow of condensed hot water into a first steam component and a first water component, and forming the first flow of fluid comprising the first steam component or at least a part of the first steam component. This way, the first heat exchanger will be fed by steam having a lower temperature than the steam fed to the second heat exchanger. Therefore, the first heat exchanger also has the function of a pre-heater in this alternative, which improves the efficiency of the heating. In both of the alternatives the first heat exchanger is positioned upstream from the second heat exchanger with respect to the flow of the superheated steam, which means that the heat exchanger assembly has the function of a parallel heat exchanger in which the temperature gradient of the heat exchanger is decreasing with an increasing temperature gradient of the superheated steam, which improves the efficiency of the heating.
The method according to the first aspect of the present invention may further comprise leading a second flow of fluid from the first heat exchanger, the second flow of fluid comprising water from the first flow of fluid, and separating a second steam component and a second water component from the second flow of fluid. This separation gives further control over the energy transfer in the system.
The supplier of pressurized steam may be a boiler, and the method may further comprise forming a third flow of fluid from the second water component, leading the third flow of fluid to the boiler, and generating at least a portion of the pressurized steam from the third flow of fluid in the boiler. This means that the water fed to the boiler will be pre-heated from waste heat generated in the drying, which will improve the overall energy efficiency of the drying.
The term “guide plate” as used in the present specification is to be understood as a generic term including evidently technical solutions encompassed by the literal understanding of the term, and also plates or walls serving to divide the closed container into several compartments and serving to control the transfer and transport of the moist particulate material within the cylindrical parts of the closed container, and in particular to control the time of rest of the particulate material in the individual compartments and as described per se in several of the above listed patent applications and patents.
The term “upright” as used in the present specification is to be understood as a generic term including evidently technical solutions encompassed by the literal understanding of the term, and also orientations which are not strictly vertical, however, differing from a horizontal orientation and also including sloping orientations defined by the guide plate or guide plates.
The expression “a plurality of guide plates positioned upright and circumferentially around the heat exchanger” as used in the present specification is to be understood as encompassing not only the literal understanding of the expression, but also technical solutions such as guide plates having any geometrical configuration, including planer plates, curved or partially curved and planar plates, or plates including one or more sections which are bent along a straight or curved line from the orientation of the remaining part of the plate, and in addition, the upright position of the plate is to encompass any overall orientation of the plate relative to the supporting horizontal plane, e.g., defined by the geometrical center line of the geometrical structure or the plane defined by a part, in particular the major part, of the guide plate.
The method according to the first aspect of the present invention may further comprise forming a fourth flow of fluid from the flow of condensed hot water, leading the fourth flow of fluid to the primary flow of steam, and mixing the fourth flow of fluid into the primary flow of steam. The mixing will have the effect that the temperature and/or pressure of the pressurized steam is lowered to be suitable for the steam dryer, which means that the supplier of steam can deliver steam with a higher temperature and/or pressure that is suitable for other applications, for example driving a turbine. This will improve the overall efficiency of the system.
The method according to the first aspect of the present invention may further comprise forming a fifth flow of fluid from the first water component and/or leading a sixth flow of fluid from the first heat exchanger comprising water condensed from the first flow of fluid, and separating a third steam component and a third water component from the fifth flow of fluid and/or the sixth flow of fluid. This separation gives further control over the energy transfer in the system.
The supplier of pressurized steam may be a boiler, and the method may further comprise forming a seventh flow of fluid from the third water component, leading the seventh flow of fluid to the boiler, and generating at least a portion of the pressurized steam from the seventh flow of fluid in the boiler. This means that the water fed to the boiler will be pre-heated from waste heat generated in the drying, which will improve the overall energy efficiency of the drying.
The method according to the first aspect of the present invention may further comprise forming an eighth flow of fluid from the first water component, leading the eighth flow of fluid to the primary flow of steam, and mixing the eighth flow of fluid into the primary flow of steam. The mixing will have the effect that the temperature and/or pressure of the pressurized steam is lowered to be suitable for the steam dryer, which means that the supplier of steam can deliver steam with a higher temperature and/or pressure that is suitable for other applications, for example driving a turbine. This will improve the overall efficiency of the system.
The method according to the first aspect of the present invention may further comprise providing a primary evaporation unit for reducing the water content of a first juice comprising sugar, and leading a first exhaust flow from the closed container to the primary evaporation unit for heating the primary evaporation unit, the first exhaust flow comprising steam from the superheated steam.
The method according to the first aspect of the present invention may further comprise providing a secondary evaporation unit for reducing the water content of a second juice comprising sugar, and supplying a secondary flow of steam from the supplier to the secondary evaporation unit for heating the secondary evaporation unit.
The method according to the first aspect of the present invention may further comprise providing the first juice as input to the primary evaporation unit, providing the second juice as output from the primary evaporation unit, the second juice comprising sugar from the first juice, and providing the second juice as input to the secondary evaporation unit.
The method according to the first aspect of the present invention may further comprise providing a tertiary evaporation unit for reducing the water content of a third juice comprising sugar, and/or leading a second exhaust flow from the primary evaporation unit to the tertiary evaporation unit for heating the tertiary evaporation unit, the second exhaust flow comprising steam evaporated from the first juice, and/or leading a third exhaust flow from the secondary evaporation unit to the tertiary evaporation unit for heating the tertiary evaporation unit, the third exhaust flow comprising steam evaporated from the second juice.
The method according to the first aspect of the present invention may further comprise providing the third juice as output from the secondary evaporation unit, the third juice comprising sugar from the second juice, and providing the third juice as input to the tertiary evaporation unit.
The method according to the first aspect of the present invention may further comprise forming a ninth flow of fluid from the second steam component, and leading the ninth flow of fluid to the secondary evaporation unit for heating the secondary evaporation unit.
The method according to the first aspect of the present invention may further comprise forming a tenth flow of fluid from the third steam component, and leading the tenth flow of fluid to the secondary evaporation unit for heating the secondary evaporation unit.
The above objects are according to a second aspect of the present invention are achieved by a system of drying humid particulate material, the system comprising: a supplier of pressurized steam and a steam dryer for drying the humid particulate material;
the steam dryer comprising: a closed container for maintaining an atmosphere comprising superheated steam at an elevated pressure, the closed container comprising a lower cylindrical part and an upper cylindrical part; a heat exchanger assembly located inside the closed container and comprising a channel for allowing the superheated steam to be transported from inside the upper cylindrical part to inside the lower cylindrical part, the heat exchanger assembly comprising a first heat exchanger and a second heat exchanger for heating the superheated steam, the first heat exchanger being positioned above the second heat exchanger and the channel going down through the first and second heat exchangers; an impeller for generating a flow of the superheated steam going upward on the outside of the heat exchanger assembly to the inside of the upper cylindrical part and downward through the channel; a material inlet for feeding the moist particulate material into the lower part of the closed container; a plurality of guide plates positioned upright and circumferentially around the heat exchanger for guiding the moist particulate material along a path around the heat exchanger assembly for subjecting the moist particulate material to the flow of the superheated steam for converting the moist particulate material into dry particulate material; and a material outlet for removing the dry particulate material from the closed container; and
the system further comprising: a first steam conduit for supplying a primary flow of steam from the supplier to the second heat exchanger for heating the second heat exchanger and the second heat exchanger being adapted for condensing the primary flow of steam into a flow of condensed hot water; a hot water outlet for discharging the flow of condensed hot water from the second heat exchanger; a first flow generator for generating a first flow of fluid exclusively from the flow of condensed hot water; and a first fluid conduit for leading the first flow of fluid to the first heat exchanger for heating the first heat exchanger.
The first flow generator may be adapted for forming the first flow of fluid comprising the flow of condensed hot water or at least a part of the condensed hot water. Alternatively, the first flow generator may comprising: a first flasher for separating the flow of condensed hot water into a first steam component and a first water component, and the first flow generator may be adapted for forming the first flow of fluid comprising the first steam component or at least a port of the first steam component.
The system according to the first aspect of the present invention may further comprise a second fluid conduit for leading a second flow of fluid from the first heat exchanger to a second flasher for separating a second steam component and a second water component from the second flow of fluid, the second flow of fluid comprising water from the first flow of fluid.
The supplier of pressurized steam may be a boiler, the second flasher further may be adapted for forming a third flow of fluid from the second water component, and the system may further comprise a third fluid conduit for leading the third flow of fluid from the second flasher to the boiler, and the boiler may be adapted for generating at least a portion of the pressurized steam from the third flow of fluid in the boiler.
The first flow generator may further be adapted for forming a fourth flow of fluid from the flow of condensed hot water, the system may further comprise a fourth fluid conduit for leading the fourth flow of fluid from the second flasher to the primary flow of steam, and a first mixer for mixing the fourth flow of fluid into the primary flow of steam.
The first flasher may further be adapted for forming a fifth flow of fluid from the first water component, and the system may further comprise a third flasher; a fifth fluid conduit for leading the fifth flow of fluid from the first flasher to the third flasher, and/or a sixth fluid conduit for leading a sixth flow of fluid from the first heat exchanger to the third flasher, the sixth flow of fluid comprising water condensed from the first flow of fluid, and the third flasher being adapted for separating a third steam component and a third water component from the fifth flow of fluid and/or the sixth flow of fluid.
The supplier of pressurized steam may be a boiler, the third flasher may further be adapted for forming a seventh flow of fluid from the third water component, and the system may further comprise a seventh fluid conduit for leading the seventh flow of fluid from the third flasher to the boiler, and the boiler may further be adapted for generating at least a portion of the pressurized steam from the seventh flow of fluid in the boiler.
The first flasher may further be adapted for forming an eighth flow of fluid from the first water component, and the system may further comprise an eighth fluid conduit for leading the eighth flow of fluid from the third flasher to the primary flow of steam, and a second mixer for mixing the eighth flow of fluid into the primary flow of steam.
The system according to the second aspect of the present invention may further comprise a primary evaporation unit for reducing the water content of a first juice comprising sugar, and a first exhaust conduit for leading a first exhaust flow from the closed container to the primary evaporation unit for heating the primary evaporation unit, the first exhaust flow comprising steam from the superheated steam.
The system according to the second aspect of the present invention may further comprise a secondary evaporation unit for reducing the water content of a second juice comprising sugar, and a second steam conduit for supplying a secondary flow of steam from the supplier to the secondary evaporation unit for heating the secondary evaporation unit.
The system according to the second aspect of the present invention may further comprise a first juice conduit for leading the first juice to the primary evaporation unit, a first juice inlet for receiving the first juice as input to the primary evaporation unit, a first juice outlet for removing the second juice as output from the primary evaporation unit, the second juice comprising sugar from the first juice, a second juice conduit for leading the second juice to the secondary evaporation unit, and a second juice inlet for receiving the second juice as input to the secondary evaporation unit.
The system according to the second aspect of the present invention may further comprise a tertiary evaporation unit for reducing the water content of a third juice comprising sugar, and a second exhaust conduit for leading a second exhaust flow from the primary evaporation unit to the tertiary evaporation unit for heating the tertiary evaporation unit, the second exhaust flow comprising steam evaporated from the first juice, and a third exhaust conduit for leading a third exhaust flow from the secondary evaporation unit to the tertiary evaporation unit for heating the tertiary evaporation unit, the third exhaust flow comprising steam evaporated from the second juice.
The system according to the second aspect of the present invention may further comprise a second juice outlet for removing the third juice as output from the secondary evaporation unit, the third juice comprising sugar from the second juice, a third juice conduit for leading the third juice to the tertiary evaporation unit, and a third juice inlet for receiving the third juice as input to the tertiary evaporation unit.
The second flasher may further be adapted for forming a ninth flow of fluid from the second steam component, and the system may further comprise a ninth fluid conduit for leading the ninth flow of fluid to the secondary evaporation unit for heating the secondary evaporation unit.
The third flasher may further be adapted to form a tenth flow of fluid from the third steam component and the system may further comprise a tenth fluid conduit for leading the tenth flow of fluid to the secondary evaporation unit for heating the secondary evaporation unit.
The system according to the second aspect of the present invention may further comprise a generator for generating electricity, and said second steam conduit may comprise a generator for being driven by said secondary flow of steam for driving said generator.